testing xsi:type with ruby 1.8 xml parser

test-xsi-type.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'crack'

xmldoc = <<-doc
<root-node>
  <child-node xsi:type = "mytypecast">data</child-node>
</root-node>
doc

c = Crack::XML.parse xmldoc
p c.to_hash

__END__
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rexml/parsers/baseparser.rb:389:in `pull': Undefined prefix xsi found (REXML::UndefinedNamespaceException)
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/set.rb:195:in `each'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/set.rb:195:in `each_key'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/set.rb:195:in `each'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rexml/parsers/baseparser.rb:387:in `pull'
	from /Library/Ruby/Gems/1.8/gems/crack-0.3.1/lib/crack/xml.rb:198:in `parse'
	from /Library/Ruby/Gems/1.8/gems/crack-0.3.1/lib/crack/xml.rb:229:in `parse'
	from test-xsi-type.rb:12